1. Field of the Invention
The present invention relates to a cleaning apparatus, and more particularly, to a cleaning apparatus capable of cleaning narrow surfaces such as an inner surface of a bottom (i.e., reactor bottom) of a reactor pressure vessel in a boiling water reactor (BWR).
2. Description of the Related Art
The bottom portion of the reactor pressure vessel of a boiling water reactor has a hemispherical shape, and accordingly, in such a reactor bottom portion, it is unavoidable to accumulate dust or like containing radioactive substances. In order to clean the dust on the inner surface of the reactor bottom portion, it will be necessary to insert a suction hose in a reactor pressure vessel so as to extend to the reactor's inner bottom surface to thereby suck the dust together with reactor water.
As such a cleaning apparatus, there have been proposed a reactor bottom cleaning apparatus as disclosed in Japanese Patent Laid-Open Publication No. 2004-354053: Patent Document 1) and an in-core cleaning apparatus as disclosed in Japanese Patent Laid-Open Publication No. 8-122484: Patent Document 2).
The reactor bottom cleaning apparatus described in Patent Document 1 includes a rotary suction device, which is equipped with a suction port facing the reactor bottom, and which rotates at a constant radius with respect to the body of the apparatus within a predetermined plane by using a rotary actuator, for example.
On the other hand, the in-core cleaning apparatus described in Patent Document 2 has an operating pole from which a support pole and a crown unit are brunched. When the operating pole is rotated around its axis, the support pole rotates within a predetermined plane at a constant radius around the crown unit mounted on a jet pump so as to move a suction hose attached to the support pole.
However, a large number of short stubs (CRD stubs) are installed in a protruding condition at predetermined intervals on the reactor bottom to allow penetration of a control rod drive mechanism (hereinafter referred to as a CRD or CRD mechanism). Furthermore, an in-core monitor housing (ICM housing) is also installed on the reactor bottom to insert an in-core monitor (hereinafter referred to as an ICM).
Consequently, it is extremely troublesome to thoroughly clean between CRD stubs or around the ICM housing by means of a suction hose, requiring a great deal of time and effort.
Both the cleaning apparatus described in Patent Documents 1 and 2 require to rotate the suction port or suction hose at a constant radius within a predetermined plane. Even with these cleaning apparatus, a large number of protrusions including the CRD stubs and ICM housing get in the way of cleaning, inevitably taking a great deal of time and effort to clean the inner surface of the reactor bottom.
For example, the apparatus described in Patent Document 1 may clean between the CRD stubs by rotating the rotary suction device equipped with the suction port within a range of movement. However, in order to thoroughly clean an area accessible to the rotary suction device, it is required to rotate the rotary suction device while attentively moving the body of the apparatus equipped with the rotary suction device.